Definition of NNT/NNH

Definition of NNT/NNH - The Efficacy Scorecard

• Number Needed to Treat (NNT): The average number of patients who need to be treated to prevent one additional bad outcome.

  • A measure of a therapy's effectiveness.
  • Formula: $NNT = 1 / ARR$ (Absolute Risk Reduction).
  • A low NNT indicates a more effective intervention.
  • Conventionally rounded up to the next whole number.

• Number Needed to Harm (NNH): The average number of patients who need to be treated for one additional person to be harmed.

  • A measure of a therapy's potential for harm.
  • Formula: $NNH = 1 / ARI$ (Absolute Risk Increase).
  • A low NNH indicates a higher risk of harm.
  • Conventionally rounded down to the nearest whole number.

• Interpretation:
  • The ideal intervention has a ↓ low NNT and a ↑ high NNH.
  • Provides a direct measure of the real-world impact of a clinical choice.

⭐ NNT is a more clinically intuitive metric than relative risk. It helps in communicating the likelihood of a treatment's benefit to a patient in tangible terms (e.g., "We need to treat 10 people like you for one person to benefit").

High-Yield Points - ⚡ Biggest Takeaways

• NNT (Number Needed to Treat) is the average number of patients who must be treated to prevent one additional adverse outcome.
• NNH (Number Needed to Harm) is the number of individuals who must be exposed to a risk factor to cause one additional adverse outcome.
• NNT is the reciprocal of the Absolute Risk Reduction (ARR); NNT = 1/ARR.
• NNH is the reciprocal of the Attributable Risk (AR); NNH = 1/AR.
• A low NNT indicates a more effective treatment.
• A high NNH indicates a safer intervention.